The overall objective of the first portion of this project is to characterize accurately all components of norepinephrine (NE) inactivation in vascular tissue. The experiments are performed on rabbit aorta because the neuronal and extraneuronal components of NE inactivation can be physically separated in this tissue. During the coming year, effort will center on the development of model systems for studying the neuronal and extraneuronal transport systems. Experiments will be performed with various doses of inhibitors of monoamine oxidase, catechol-O-methyl transferase, and granular uptake to find a pretreatment which will block removal of NE from the cytoplasm without affecting its uptake by the transport system in the cell membrane. The second portion of this work deals with the uptake of tyrosine by adrenergic nerve terminals. This process is very difficult to study in most sympathetically innervated organs because the nerve terminals represent such a small proportion of the tissue. However, in the adventitia of rabbit aorta tyrosine uptake by nerve terminals may represent a significant proportion of total tissue uptake. During the coming year, an attempt will be made to determine whether this is so by using rabbits pretreated with 6-hydroxy dopamine.